Percentage Calculator
Solve four common percent questions in one tool. Switch modes to handle any percentage scenario.
Calculator
20.00 ÷ (50.00 ÷ 100) = 40.0000
How percentage math works
All four modes use the same underlying definition: a percent is a ratio expressed per hundred. The four formulas this tool implements are: percent-of (X% of Y = X ÷ 100 × Y), is-what-percent (X ÷ Y × 100), is-percent-of-what (X ÷ (Y ÷ 100)), and percent-change ((Y − X) ÷ X × 100). Each mode is just an algebraic rearrangement of the same identity, so picking the right mode is a matter of asking which value you have and which one you want to find.
Why use this calculator?
Four modes in one page means no bouncing between bookmarks when the question changes. The calculator runs entirely in your browser with no tracking and no signup, every result is encoded in the URL so you can share or save the exact calculation, and the math layer is the same primitive used by spreadsheets and statistics tools the world over.
FAQ
Is this percentage calculator free?
Yes. Every calculator on Nulumia is free to use, runs in your browser, and never sends your numbers to a server. There is no account, no signup, and no usage limit.
Which mode should I use?
Use 'percent of a number' when you have a percent and a total and want the part. Use 'X is what percent of Y' when you have two numbers and want their ratio as a percent. Use 'X is Y% of what' when you know the part and the percent and want the original total. Use 'percent change' when comparing a before-and-after value (sales growth, weight change, score improvement).
How is percent change calculated?
Percent change is (new − old) ÷ old × 100. A value going from 80 to 100 is a 25% increase; going from 100 to 80 is a 20% decrease. The denominator is always the starting value, which is why the same absolute change can yield different percentage figures depending on direction.
What if my total is zero?
Division by zero is undefined, so the calculator returns zero in those modes (X is what % of 0; X is 0% of what; percent change from 0). The result field will show 0 — interpret it as 'undefined' rather than a meaningful value.